Recent miniaturization and sophistication of electronic apparatus serve to encourage a chip mounting method to connect a semiconductor chip directly to a substrate without using a package. There is also known a solid state imaging device whose semiconductor chip (solid-state image sensor) is mounted, by this chip mounting method, to curve on a substrate so as to correct the aberration of a taking lens (see, Japanese Patent Laid-open Publication No. 2003-188366).
The substrate of this solid state imaging device has an upper surface that is spherically-curved to correspond to the curvature of field of the taking lens. Additionally, the solid-state imaging device is made thin, and follows the curved upper surface of the substrate when bonded thereto. This curved solid-state image sensor can achieve a good focusing state throughout the image plane even when combined with a simple taking lens.
Meanwhile, in order to improve an aperture ratio (light receiving efficiency), there is known a solid-state image sensor of back illuminated type which has a light receiving surface on a back side opposite to a front side provided with electrode pads. Because of the structure to receive light on the back side, the back illuminated type image sensors are made thinner than the general front illuminated type image sensors, so that the incident light on the back side can easily reach photodiodes contained in the image sensor. This means that the back illuminated type image sensors are flexible and easily curved.
However, even if the easily-curved back illuminated type image sensor is used, the solid state imaging device of the Publication No. 2003-188366 still has the problem that the curved upper surface is hard to shape on the substrate. If the substrate is a functional device to process the signals from the image sensor, the curved upper surface is especially difficult to shape.